1. Field of the Invention
The present invention relates to pigment ink which permits printing with an increased density and an ink jet recording method, an ink cartridge, ink jet device and ink jet recording apparatus which is capable of recording by discharging the ink droplets from the orifices of a recording head with the aid of the function of heat energy.
2. Related Background Art
An ink jet recording method has several advantages in that the method produces low noise and can obtain a high-resolution recorded image at a high speed by utilizing a highly integrated head.
Such an ink jet recording method uses as ink a solution obtained by dissolving one of various water-soluble dyes in water or a solvent mixture of water and an organic solvent. Because the water-soluble dye exhibits poor light resistance, when such a water-soluble dye is used, the light resistance of the recorded image frequently becomes a problem. In addition, because the ink is soluble in water, the water resistance of the recorded image also frequently becomes a problem. Namely, when rain, sweat or drinking water is applied to the recorded image, the recorded image is blurred with the ink or even disappears in some cases.
On the other hand, because writing utensils such as ball point pens, which use dyes, encounter the same problem, various kinds of aqueous pigment ink for writing utensils have been proposed for resolving the problems with respect to light resistance and water resistance.
Examples of studies, which investigated dispersion stability, prevention against solidification of ink at the end of a pen, and prevention against abrasion of the ball of a ball point pen, include those disclosed in Japanese Patent Laid-Open Nos. 58-80368, 61-272278, 62-568, 62-101671 and 62-101672. Ball point pens and markers, which use aqueous pigment ink, have recently been brought to the market.
Japanese Patent Laid-Open Nos. 64-6074 and 64-31881 disclose aqueous pigment ink at a pH of 5.0 or less which uses carbon black.
When conventional aqueous pigment ink for writing utensils is used in an ink jet recording device of the type in which recording is made by discharging an ink from the orifices of a recording head as a stream of ink droplets, however, there is a problem in that the discharging stability is significantly deteriorated, and printing failure occurs.
Particularly, when the conventional pigment ink is used in an ink jet recording device of the type in which ink droplets are discharged by applying heat energy to the ink, deposits are produced on a thin film resistor (heater) due to the heat pulse applied to the ink, thereby causing incomplete foaming of the ink and thus the occurrence of a disturbance resulting in non-uniform discharging. Even when no deposit is produced on the thin film resistor (heater), incomplete foaming still may occur and inhibits discharging of the droplets in response to the pulse applied to the ink and thus causes non-discharging.
Namely, in order to stably discharge the ink from the end of an orifice, the ink must have the ability to foam with a desired volume on the thin film resistor and repeat foaming and defoaming within a desired time. Because the conventional ink for writing utensils does not have such an ability, the ink produces the above-described problems when being charged in an ink jet recording device and used for recording.
Further, when a pigment ink, which has been previously proposed and which uses carbon black, is used in ink jet recording, although the fastness of the image printed on plain paper is significantly improved, as compared with that of the image printed by using dye ink, later research reveals that there is a disadvantage in that the density of the printed image, which is a characteristic of ink jet recording, is inferior to that of the image printed by using dye ink. If the pigment concentration is increased to improve the printing density, there is a default in that the discharging stability significantly deteriorated.
Because printing ink can be used at an extremely high concentration, as compared with the ink used in an ink jet recording device in the present invention, the printing density can be easily increased. The density can be also increased by increasing the thickness of the coated ink layer. However, in ink jet recording, particularly, high-density recording, because the size of the orifice is very small, the amount of the ink discharged is limited. In addition, as described above, an increase in the concentration of the pigment contained in the ink causes the occurrence of undesirable troubles in that precipitates during long-term preservation so that the ink solidifies due to drying at the end of the orifice, and non-discharging thus occurs. Furthermore, although some of the conventional aqueous pigment inks have excellent discharging properties for a relatively short time, the conventional pigment ink has a problem in that the ink is unstably discharged and finally not discharged when the driving conditions of the recording head are changed or when the ink is continuously discharged for a long time.